Here's another wrinkle.
Brokers are not required to create 1099-Bs for "same day" sales so you may or may not get a 1099-B for the stock sold "for taxes." If you don't get a 1099-B you don't have to report the sale, but you might want to anyway as the typical same day sale creates a small loss due to selling commissions and fees.
It's important to understand that same day sales - either yours or the stock sold for taxes - generally create a small loss. That's because the vesting of the RSU creates compensation (GROSS number of shares vesting x per share "fair market value" at the vesting date) and that compensation becomes your basis for the GROSS number of shares. So if you sell those shares on the same day the shares vest the selling price is usually pretty close to that "fair market value" used by your employer so you'd expect a loss because of the cost of selling.
